t := "haystack needle haystack" // "text" - thing we search in
p := "needle" // "pattern" - thing we search for

func naive(p, t string) []int {
    // assume len(p) <= len(t)
    occurrences := []int{}
    for i := 0; i < len(t) - len(p) + 1; i++ { // for each alignment of p to t
        match := true  // assume we match until proven wrong
        for j := 0; j < len(p); j++ { // for each position of p
            if t[i+j] != p[j] {
                match = false  // at least 1 char mismatches
                break
            }
        }
        if match {
            occurrences = append(occurrences, i)
        }
    }
    return occurrences
}

naive(p, t)

t[9:9+len(p)]

naive("needle", "needleneedleneedle")